Avalanche Forecast

Archived

Jan 29th, 2016–Jan 30th, 2016

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Olympics.

In the Olympics, the main problem has shifted to new areas of wind slab on lee wind exposed terrain, near and above treeline. Wind slabs may have formed on a variety of aspects due to highly variable wind directions. Watch for new cornices near ridges.

Detailed Forecast

Cool weather with light snow showers and moderate westerly winds should allow for an overall slowly decreasing danger.

The greatest avalanche problem should be sensitive wind slabs on lee slopes, mainly W-N-E facing slopes, especially below ridges, near and above treeline.

Watch for newly formed cornices along ridges as well. These may be sensitive to human triggers.

Below treeline, the old wet snowpack should continue to drain, and refreeze forming a new crust. Watch for open creeks which were reported to be quite deep in areas, below treeline.

Snowpack Discussion

Heavy rain fell in the Olympics Wednesday afternoon through Thursday morning to at least 7500 feet. Over 2 inches of rain was recorded at the Hurricane Ridge weather station by Thursday midday. This rain event should give the snowpack a new horizon going forward.

A strong cold front passed the area Friday depositing about 6-8 inches of new snow by Friday afternoon. The new snow has fallen with very strong and shifting winds creating both new shallow wind slabs near ridges and sensitive new cornices.

NWAC observer, Matt Schonwald travelled near and below treeline Friday and found cracks in the newly forming wind slabs on a variety of aspects due to swirling winds. Also, new cornices were sensitive to trigger, but still relatively small.

As expected in this region, the bonding of the new snow to the forming crust was reportedly very strong. There was, however, a thin layer of low density stellar crystals above the crust, forming the weak layer for newly forming wind slabs to fail.

These conditions should produce some sensitive human triggered avalanches on wind loaded terrain until those layers have time to settle and stabilize, mainly near or above treeline.

In the below treeline zone, a strong crust with shallow new snow should allow for improving conditions, but watch for shallow wind deposited snow on isolated features, such as cross loaded ribs or slopes convexities.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.